1. Technical Field of the Invention
The present invention relates generally to a spark plug for internal combustion engines such as automotive gasoline engines, and more particularly to an improved structure of such a spark plug equipped with a stream shaper working to shape tumble vortexes into streams oriented inside a combustion chamber of the engine to enhance the ignitability of air-fuel mixture.
2. Background Art
There have been proposed various types of spark plugs designed to have improved structures and materials of a center electrode and/or a ground electrode for enhancing the ignitability of air-fuel mixture within a combustion chamber of the engine. For example, Japanese Patent First Publication No. 2005-63705 teaches geometrical configuration and material of the center electrode of the spark plug for improving the heat-resistance and wear-resistance thereof.
In typical internal combustion engines, streams of air-fuel mixture flowing through parts of the spark plug such as the center electrode and the ground electrode exposed to a combustion chamber of the engine are usually disturbed by tumble vortexes of the air-fuel mixture, thus resulting in the instability in creating a sequence of sparks between the center and ground electrodes. In recent years, internal combustion engines have appeared in which the configuration of intake ports or piston heads are modified in order to enhance the power output from the engine, so that the speed of streams of the air-fuel mixture is increased, thus resulting in increased dispersion of the tumble vortexes. This leads to instability of size or orientation of the sparks. The flame of the mixture, as created in the combustion chamber, may be undesirably cooled or dispersed depending upon the orientation of a flow of the spark, thus resulting in undesired form of the flame which contributes to poor ignition of the mixture. The structure of the spark plug, as taught in the above publication, has the same problem, as described above.